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ID: 358793.0, MPI für Astronomie / Publikationen_mpia
The substellar mass function in s Orionis. II. Optical, near-infrared and IRAC/Spitzer photometry of young cluster brown dwarfs and planetary-mass objects
Authors:Caballero, J. A.; Béjar, V. J. S.; Rebolo, R.; Eislöffel, J.; Zapatero Osorio, M. R.; Mundt, R.; Barrado Y Navascués, D.; Bihain, G.; Bailer-Jones, C. A. L.; Forveille, T.; Martín, E. L.
Date of Publication (YYYY-MM-DD):2007
Title of Journal:Astronomy and Astrophysics
Start Page:903
End Page:918
Audience:Not Specified
Abstract / Description:Aims.We investigate the mass function in the substellar domain down to a few Jupiter masses in the young sigma Orionis open cluster (3±2 Ma, d = 360^+70_-60 pc). Methods: We have performed a deep IJ-band search, covering an area of 790 arcmin2 close to the cluster centre. This survey was complemented with an infrared follow-up in the HK_s- and Spitzer 3.6-8.0 mum-bands. Using colour-magnitude diagrams, we have selected 49 candidate cluster members in the magnitude interval 16.1 mag < I < 23.0 mag. Results: Accounting for flux excesses at 8.0 mum and previously known spectral features of youth, we identify 30 objects as bona fide cluster members. Four are first identified from our optical-near infrared data. Eleven have most probable masses below the deuterium burning limit which we therefore classify as candidate planetary-mass objects. The slope of the substellar mass spectrum (Delta N / Delta {M} ≈ a { M}-alpha) in the mass interval 0.11 M_o < {M} < 0.006 M_o is alpha = +0.6 ± 0.2. Any mass limit to formation via opacity-limited fragmentation must lie below 0.006 M_o. The frequency of sigma Orionis brown dwarfs with circumsubstellar discs is 47±9 %. Conclusions: The continuity in the mass function and in the frequency of discs suggests that very low-mass stars and substellar objects, even below the deuterium-burning mass limit, share the same formation mechanism. Alexander von Humboldt Fellow at the Max-Planck-Institut für Astronomie Appendices are only available in electronic form at
Free Keywords:stars: low mass; brown dwarfs; Galaxy: open clusters and associations: individual: σ Orionis; stars: planetary systems: protoplanetary discs
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie

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